Based on the data provided, we can observe that the coin in question has had a starting price in previous auctions ranging from 12.12 euros to 78.93 euros. The average auction closing price has been 33.47 euros, with a conservation grade of 80 (MBC+).

Considering that the starting price in this auction is 20 euros and the average closing price has been 33.47 euros, we could estimate a maximum purchase price around that value. Given that the coin's conservation grade is 80 (MBC+), we can consider it to be in good condition, which could influence a higher closing price.

Therefore, an estimated maximum purchase price for this coin in the next auction could be around 35-40 euros, considering the information provided and the history of prices from previous auctions.